EP2531556A1

EP2531556A1 - Plastic substrates having a scratch-resistant coating, in particular housings of electronic devices, having high transparency, method for the production thereof, and use thereof

Info

Publication number: EP2531556A1
Application number: EP10760933A
Authority: EP
Inventors: Jan Bernd Kues; Andre Brosseit; Karin Homann; Stefanie Schroeder
Original assignee: BASF Coatings GmbH
Current assignee: BASF Coatings GmbH
Priority date: 2010-02-04
Filing date: 2010-10-02
Publication date: 2012-12-12
Anticipated expiration: 2030-10-02
Also published as: CN102712783B; WO2011095186A1; CN102712783A; US20130202892A1; EP2531556B1; US9017819B2; JP2013518943A; DE102010006755A1; JP5744064B2

Abstract

The invention relates to a method for coating plastic substrates, a transparent coating agent comprising at least one radiation-curable binder (A), nanoparticles (B), reactive diluent (C), and optionally solvent being applied to the plastic substrate, characterized in that the coating agent contains (i) 30 to 60 wt %, relative to the total weight of the components (A1), (A2), (A3), (B), (C1), (C2), and (C3), of the nanoparticles (B), (ii) 15 to 40 wt % of one or more urethane (meth)acrylates (A1) having on average 3 to 5 acrylate and/or methacrylate groups per molecule, (iii) 0 to less than 10 wt % of one or more urethane (meth)acrylates (A2) having on average more than 5 acrylate and/or methacrylate groups per molecule, (iv) 0 to less than 10 wt % of one or more urethane (meth)acrylates (A3) having on average less than 3 acrylate and/or methacrylate groups per molecule, (v) 55 to 80 wt % of one or more monomeric and/or oligomeric compounds (C1) differing from the components (A1), (A2), and (A3) and having 4 acrylate and/or methacrylate groups per molecule, (vi) 0 to 15 wt % of one or more monomeric and/or oligomeric compounds (C2) differing from the components (A1), (A2), and (A3) and having 2 acrylate and/or methacrylate groups per molecule, and (vii) 0 to 15 wt % of one or more monomeric and/or oligomeric compounds (C3) differing from the components (A1), (A2), and (A3) and having 3 acrylate and/or methacrylate groups per molecule, wherein the sum of the weight fractions of the film-forming components (A1), (A2), (A3), (C1), (C2), and (C3) is 100 wt %. The invention further relates to the coated polycarbonate substrates obtainable by the method and to the use thereof.

Description

Scratch-resistant coated plastic substrates, in particular housings of electronic devices, with high transparency. Process for their preparation and their use

The present invention relates to a method for coating plastic substrates, in particular of housings of electronic devices, in which a transparent coating composition comprising at least one radiation-curable (Jrethan (meth) acrylate (A), nanoparticles (B), reactive diluents (C) and optionally solvents is applied to the plastic substrate, as well as the coated substrates obtainable by the process.

From WO 09/049000 a method of the type mentioned above is already known, are used in the radiation-curable coating compositions, in addition to> 10 to <40 wt .-% nanoparticles (B), based on the total weight of the film-forming components (A) and (C), 10 to 60 wt .-% of at least one binder (A) and 40 to 90 wt .-% of at least one reactive diluent (C), wherein the sum of the weight fractions of the film-forming components (A) and (C) each 100th Wt .-% is. The resulting coatings are distinguished by good abrasion resistance and very good optical properties, ie a low haze value of the unloaded coating of less than 1. This is ensured in accordance with WO09 / 049000 by using urethane (meth) acrylates having 2 double bonds per molecule as binder (A) and high-functional reactive diluents having preferably 3 to 6 double bonds per molecule as reactive diluents (C). On the other hand, hexafunctional urethane (meth) acrylates and difunctional reactive diluents, such as hexanediol diacrylate, or only trihydric and pentafunctional reactive diluents used, the required very low Haze values are not achieved.

Furthermore, EP-B-1 704 189 discloses radiation-curable coating compositions for the coating of plastic substrates, in particular of polycarbonate substrates, which in addition to nanoparticles (B) comprise at least two different polyfunctional (meth) acrylate-functional compounds, in particular a mixture of a hexafunctional urethane acrylate and at least one compound selected from the group consisting of butanediol diacrylate, trimethylolpropane triacrylate and pentaerythritol triacrylate. This combination of two different polyfunctional (meth) acrylate-functional compounds improves the abrasion resistance of the resulting cured coating compared to cured coatings based on only one polyfunctional (meth) acrylate-functional compound each. However, information on the optical properties of the resulting coatings and on the influence of the film-forming components on the optical properties is lacking in this document.

Furthermore, radiation-curable coating compositions for the coating of plastic substrates, in particular of polycarbonate substrates, which in addition to nanoparticles (B) are at least two known from the conference report "RadTech 2000" from April 9-12, 2000, Baltimore, pages 822-831 various polyfunctional (meth) acrylate-functional compounds, in particular a mixture of a hexafunctional urethane acrylate and at least one compound selected from the group consisting of hexanediol diacrylate, tripropylene glycol diacrylate and ethoxylated trimethylolpropane triacrylate. Furthermore, US Pat. No. 6,420,451 discloses radiation-curable coating compositions, in particular for the coating of spectacle lenses, comprising (a) 20 to 80% of a first aliphatic urethane acrylate, in particular a urethane acrylate having on average 2 double bonds per molecule, (b) 5 to 50% of a compound having one acrylate group per molecule, (c) (i) 2 to 30% of a second aliphatic urethane acrylate, in particular a urethane acrylate having on average 6 double bonds per molecule, or (ii) 2 to 25% of a multifunctional acrylate compound or ( iii) a combination of (i) and (ii) and (d) 1 to 30% nanoparticles.

EP-B-668 330 describes radiation-curable coating compositions for the coating of polycarbonate substrates which contain from 20 to 75% by weight of at least one essentially hydroxyl and isocyanate group-free aliphatic urethane acrylate (A) based on low-viscosity isocyanurate group-containing Polyisocyanates, 5 to 80% by weight of a low-viscosity acrylic ester component (C) which consists of at least 80% by weight of a bisfunctional acrylic acid ester component and up to 20% by weight of another acrylic acid ester component, and 0 to 80% by weight of a solvent or a solvent mixture, wherein the weight percentages of components (A), (C) and (LM) are each based on the total weight of components (A), (C) and (LM). However, the addition of nanoparticles to the coating compositions is not described in this document. In addition, this document lacks information on the optical properties of the resulting coatings and on the influence of the film-forming components on the optical properties. Finally, US Pat. No. 4,455,205 discloses radiation-curable coating compositions which comprise at least two different polyfunctional (meth) acrylate-functional compounds, in particular a mixture of hexanediol diacrylate and trimethylolpropane triacrylate, and the hydrolysis product of silyl-functional acrylates and colloidal silicon dioxide. However, the use of urethane (meth) acrylates in the coating compositions is not described.

task

It is an object of the present invention to provide a process for coating plastic substrates, in particular housings of electronic devices, in which the resulting coated substrates have a very high scratch resistance coupled with very high transparency and low gray haze (Haze values the unloaded coating is less than 1, preferably less than 0.8, each determined using the BYK-Gardner Haze-gard plus C4725 device). Furthermore, after application to the plastic substrates, in particular to polymethyl methacrylates, polycarbonates and / or blends of polycarbonate and other plastics, the coating compositions should not cause any swelling of the substrates. In addition, the coating compositions should lead to cured coatings having a very good adhesion (in particular determined by means of adhesive tape tear according to ASTM D 3359 and ISO 2409) on plastics, in particular on polymethyl methacrylates, polycarbonates and / or blends of polycarbonate and other plastics. Finally, the cured coatings should have a high resistance to sudden deformation (impact test), which was determined in accordance with the standard DIN EN ISO 6272-1 DE.

Solution of the task

In the light of the abovementioned task, a process has been found for coating plastic substrates, in which a transparent coating composition comprising at least one radiation-curable urethane (meth) acrylate (A), nanoparticles (B), reactive diluents (C) and, if appropriate, solvents Plastic substrate is applied, which is characterized in that the coating agent

(i) from 30 to 60% by weight, based on the total weight of the components (A1), (A2), (A3), (B), (C1), (C2) and (C3), of the nanoparticles (B) .

(ii) 15 to 40% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth) acrylates (A1) with on average 3 to 5 acrylate and / or methacrylate groups per molecule,

(iii) 0 to less than 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth ) acrylates (A2) having on average more than 5 acrylate and / or methacrylate groups per molecule,

(iv) 0 to less than 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth ) acrylates (A3) with im Means less than 3 acrylate and / or methacrylate groups per molecule,

(v) 55 to 80% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C1) having 4 acrylate and / or methacrylate groups per molecule,

(vi) 0 to 15% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C2) having 2 acrylate and / or methacrylate groups per molecule and

(vii) 0 to 15% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), one or more of the Components (A1), (A2) and (A3) containing different, monomeric and / or oligomeric compounds (C3) having 3 acrylate and / or methacrylate groups per molecule, wherein the sum of the weight fractions of the film-forming components (A1), (A2) , (A3), (C1), (C2) and (C3) each 100

Wt .-% is.

The present invention also provides the coated polycarbonate substrates obtainable by the process and their use.

In view of the prior art, it was surprising and unforeseeable for the person skilled in the art that the objects on which the present invention was based could be achieved with the aid of the method according to the invention. Thus, it is particularly surprising that coatings with a very high molecular weight are used by the combination of specific urethane acrylates with tetra-functional (meth) acrylates, if appropriate in combination with difunctional (meth) acrylic esters and / or trifunctional (meth) acrylates Scratch resistance at the same time very high transparency and low gray haze (Haze values of the unloaded coating less than 1, preferably less than 0.8, each determined using the BYK-Gardner Haze-gard plus C4725 device) can be obtained.

Furthermore, after application to the plastic substrates, in particular polymethyl methacrylates, polycarbonates and / or blends of polycarbonate and other plastics, the coating compositions do not cause any swelling of the substrates.

In addition, the coating agents lead to hardened

Coatings with very good adhesion (in particular determined by means of adhesive tape tear according to ASTM D 3359 and ISO 2409) on plastics, in particular on polymethyl methacrylates, polycarbonates and / or blends of polycarbonate and other plastics.

Finally, the cured coatings have a high resistance to sudden deformation (impact test), which was determined in accordance with the standard DIN EN ISO 6272-1 DE. Detailed description of the invention

Coating agent used according to the invention

The radiation-curable binder (A)

It is essential to the invention that the coating compositions used in the process according to the invention as radiation-curable binder (A) one or more urethane (meth) acrylates (A1) having on average 3 to 5 acrylate and / or methacrylate groups per molecule, optionally in combination with urethane acrylates (A2) containing on average more than 5 acrylate and / or methacrylate groups per molecule and / or urethane acrylates (A3) containing on average less than 3 acrylate and / or methacrylate groups per molecule. This special selection of the radiation-curable binders in combination with the tetra-functional (meth) acrylic acid esters (C1), if appropriate in combination with difunctional (meth) acrylic esters (C2) and / or trifunctional (meth) acrylic esters (C3), coatings with a very high scratch resistance at the same time very high transparency and low gray haze (Haze values of the unloaded coating less than 1, preferably less than 0.8, each determined using the BYK-Gardner Haze-gard plus C4725 device).

One or more urethane (meth) acrylates (A1) having on average 3 to 4 acrylate and / or methacrylate groups per molecule are preferably used as the radiation-curable binder (A).

In principle, all urethane (meth) acrylates (A1) with the required number of acrylate and / or methacrylate groups are suitable. While acrylate groups are preferred groups for UV curing systems, methacrylates are often cured by electron beam radiation. However, it is also possible to use urethane (meth) acrylates having both acrylate and methacrylate groups.

One or more urethane acrylates (A1) having on average 3 to 5, in particular 3 to 4, acrylate groups per molecule are preferably used as the radiation-curable binder (A). In particular, aliphatic urethane acrylates (A1) are used.

The urethane (meth) acrylates used as component (A1) can be prepared in a manner known to the person skilled in the art in that

(a1) hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates, preferably hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates having 2 to 4 C atoms in the alkyl radical, if appropriate in a blend of 0 to 50 hydroxy equivalent%, preferably with 0 to 30 hydroxy equivalent%, in each case based on the Total amount of component (a1), on other hydroxyl-containing compounds

With

(a2) one or more polyisocyanates having on average at least

3 isocyanate groups per molecule

be implemented.

The hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates of component (a1) are known hydroxyalkyl esters of acrylic and methacrylic acid. Preference is given to using hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates having 2 to 4 C atoms in the alkyl radical, for example hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate acrylate, hydroxybutyl acrylate and hydroxybutyl methacrylate, preferably hydroxyethyl acrylate is used.

If appropriate, other hydroxyl-containing compounds may also be used together with the hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates, but only hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates are preferably used as component (a1).

Suitable other hydroxyl-containing compounds are in particular monohydric to trihydric aliphatic low molecular weight alcohols, preferably having 1 to 20 C atoms, such as, for example, methanol, ethanol, n-hexanol, isooctanol, isododecanol, benzyl alcohol,

Ethylene glycol, diethylene glycol, propylene glycol, glycerol or alcohols obtained from these alcohols by alkoxylation.

The component (a2) is one or more polyisocyanates having on average at least 3 isocyanate groups per molecule, in particular aliphatic polyisocyanates having on average at least 3 isocyanate groups per molecule. Aliphatic polyisocyanates containing on average 3 to 4 isocyanate groups per molecule are preferably used.

As component (A1) it is particularly preferable to use aliphatic urethane acrylates based on isocyanurates of aliphatic diisocyanates, very particularly preferably aliphatic urethane acrylates based on isocyanurates of hexamethylene diisocyanate. These urethane acrylates are usually obtainable by reacting component (a1) with isocyanurates of aliphatic diisocyanates. isocyanates as component (a2), in particular with the isocyanurate of hexamethylene diisocyanate as component (a2).

The preparation of the urethane (meth) acrylates (A1) is generally carried out by reacting the components (a1) and (a2) by known methods, if appropriate with concomitant use of suitable urethanization catalysts. The components (a1) and (a2) are preferably reacted while maintaining an NCO / OH equivalent ratio of from 0.9: 1 to 1.1: 1, preferably about 1: 1. As a result, the resulting urethane (meth) acrylates essentially have no free hydroxyl groups and essentially no free isocyanate groups.

Suitable catalysts for the reaction are e.g. Tin (II) octoate, dibutyltin dilaurate or tertiary amines such as dimethylbenzylamine. The reaction can be carried out in bulk or else in the presence of the reactive diluents (C1), (C2) and / or (C3) or in the presence of solvent (LM), provided that these components have no hydrogen atoms reactive with isocyanate groups.

As aliphatic urethane (meth) acrylate (A1), for example, the commercially available products Sartomer CN 925 (aliphatic urethane tetraacrylate) and Sartomer CN 9276 (aliphatic urethane tetraacrylate) from Sartomer and the aliphatic urethane acrylate Desmolux ® VP LS 2308 Bayer Material Science be used.

In particular, the urethane acrylate described in EP-B-668 330 on page 2, line 41, to page 3, line 49 and in example 1 of EP-B-668 330 can also be used as component (A1) become. A urethane acrylate used with such a preference, for example, is also the commercially available urethane acrylate Desmolux® VP LS 2308 from Bayer Material Science.

Optionally, together with the urethane (meth) acrylate (A1), even small amounts of less than 10 wt .-%, based on the total weight of the film-forming components, of one or more urethane (meth) acrylates (A3) with on average less than 3 acrylate and / or methacrylate groups per molecule and / or one or more (ethane (meth) acrylates (A2) having on average more than 5 acrylate and / or methacrylate groups per molecule are used. but exclusively one or more urethane (meth) acrylates (A1) having an average of 3 to 5 acrylate and / or meth-acrylate groups per molecule used.

The urethane (meth) acrylates used as component (A2) and (A3) can be prepared analogously to the (ethane (meth) acrylates (A1) in a manner known to the person skilled in the art by using hydroxyalkyl acrylates and / or hydroxyalkyl methacrylates, preferably hydroxyalkyl acrylates and or hydroxyalkyl methacrylates having 2 to 4 C atoms in the alkyl radical, if appropriate in admixture with other hydroxyl-containing compounds, with one or more polyisocyanates having on average at least 2 isocyanate groups per

Molecule to be implemented. Aliphatic urethane acrylates are preferably used as components (A2) or (A3). The nanoparticles (B)

Particularly suitable nanoparticles (B) are oxidic inorganic nanoparticles having an average particle size of 1 to 500 nm, preferably 3 to 100 nm, particularly preferably 5 to 50 nm and very particularly preferably 5 to 30 nm. By nature, however, nanoparticles have an average particle size in the nanometer range, which makes them of particles of a middle

Particle size in the micrometer range (for example, 1 μιη and more) delineate. By "oxidically inorganic" it is meant that these are essentially nanoparticles of a metal oxide, such as aluminum oxide or a semi-metal oxide, such as silicon dioxide. The latter can be obtained, for example, from aqueous alkali metal silicate solutions by acidification and subsequent drying. Also, so-called fumed silicas obtained by flame hydrolysis of silicon halide compounds can be used. Furthermore, it is possible to hydrolyze and condense organofunctional silanes to form aqueous or aqueous-alcoholic silica sols. These can be removed by azeotropic distillation, for example, the water content. The average particle size is preferably determined by means of dynamic light scattering measurements (ALV goniometer, measuring angle 90 °, temperature 23 ° C.), the evaluation of the results being carried out by the cumulant method.

However, nanoparticles whose surface is modified with condensed compounds are particularly preferred. A surface modification is usually carried out by attaching the groups present on the nanoparticle surface, such as, for example, hydroxyl groups, to monomeric or oligomeric compounds. These monomeric or oligomeric compounds therefore contain at least one affine group opposite the groups on the nanoparticle surface. The binding can take place, for example, by covalent bonding, ionic bonding or physisorption. The part of the monomeric or oligomeric compounds not required for attachment to the nanoparticle surface preferably projects wholly or partly into the medium surrounding the nanoparticles and preferably contributes to improving the compatibility between nanoparticles on the one hand and components (A) and / or (C) on the other hand. Such nanoparticles are preferably used.

The monomeric or oligomeric compounds used for the surface modification may, in addition to the group required for attachment to the surface of the nanoparticles, also contain further functional groups which, for example, are capable of reacting with the binder component (A). Such a surface modification is achieved, for example, by adding hydrolyzable silanes which carry ethylenically unsaturated groups to the oxidic nanoparticles, preferably silicic acids or

SiO 2 sols or SiO 2 sol gels.

The surface modification of oxidic inorganic silica nanoparticles can be carried out by condensing the silanes onto the nanoparticle surface. The preparation of the nanoparticles can be carried out so that, starting from an alkali metal silicate condensation of the same under the influence of an acidic ion exchanger or an acid to the desired particle size is brought about and then optionally after stabilization of the particles, the silanes are added, whereupon these (partially) hydrolyze and at to condense the surface of the particles. The resulting sol is optionally concentrated under vacuum, by (azeotropic)

Distillation the aqueous components removed.

Surface-modified silica nanoparticles are commercially available, for example from the company Byk under the name Nanobyk or the company Nano Resins AG from Geesthacht, Germany under the name Nanopol®.

The nanoparticles (B) are preferably used dispersed in solvents.

The used reactive diluent (C)

It is essential to the invention that the coating agent used in the process contains as reactive diluent (C1) one or more monomeric and / or oligomeric compounds (C1) having 4 acrylate and / or methacrylate groups per molecule other than component (A) , In particular, the esters of acrylic and / or methacrylic acid, preferably the esters of acrylic acid, with tetrafunctional alcohols are used as component (C1).

Examples of suitable reactive diluents (C1) are pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, propoxylated pentaerythritol tetraacrylate and mixtures of said tetrafunctional reactive diluents. As component (C1) it is preferred to use pentaerythritol tetraacrylate and / or ditrimethylolpropane tetraacrylate. Reactive diluents (C2) used are one or more monomeric and / or oligomeric compounds (C2) having 2 acrylate and / or methacrylate groups per molecule other than component (A). In particular, the esters of acrylic and / or methacrylic acid, preferably the esters of acrylic acid, with difunctional alcohols are used as component (C2).

Examples of suitable reactive diluents (C2) are butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate and mixtures of the difunctional reactive diluents mentioned. Hexanediol diacrylate is preferably used as component (C2).

Reactive diluents (C3) used are one or more monomeric and / or oligomeric compounds (C3) having 3 acrylate and / or methacrylate groups per molecule other than component (A). In particular, the esters of acrylic and / or methacrylic acid, preferably the esters of acrylic acid, with trifunctional alcohols are used as component (C3).

Examples of suitable reactive diluents (C3) are trimethylolpropane triacrylate, propoxylated glycerol triacrylate, propoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate and mixtures of said trifunctional reactive diluents, with trimethylolpropane triacrylate being preferred.

The coating composition used according to the invention preferably comprises as reactive diluent a mixture of one or more tetrafunctional reactive diluents (C1) and one or more difunctional reactive diluents (C2), in particular a mixture of pentaerythritol tetraacrylate and hexanediol diacrylate.

Very particular preference is given to using in the process according to the invention coating compositions comprising as component (A1) at least one aliphatic urethane acrylate (A1) based on the isocyanate derivative of hexamethylene diisocyanate and as reactive diluent (C) a mixture of (C1) pentaerythritol tetraacrylate and (C2) hexanediol diacrylate contain.

The possibly used solvent (LM)

The coating compositions used in the process according to the invention may optionally still contain solvents. However, the solvents should be selected such that they behave as far as possible optically inert towards the polycarbonate substrate in the mixture of solvents used or when used without being mixed, and preferably do not impair this with regard to its transparency. In this sense, "inert" means that no discernable haze exists for the eye, but the term "inert" does not exclude that the solvents may selectively swell the polycarbonate substrate, which may contribute to an improvement in adhesion In addition to reducing the viscosity of the coating compositions, solvent is to permit the most uniform possible course of the coating composition on the substrate.

Particularly suitable solvents are ethanol, isopropanol, n-butanol, ethyl acetate, butyl acetate, solvent naphtha, methyl ethyl ketone, Methoxypropylacetat-2, acetone or tetrahydrofuran suitable, in particular combinations of different solvents are preferred. Particular preference is given to using combinations of the solvents ethanol, isopropanol, n-butanol, ethyl acetate, butyl acetate, methyl ethyl ketone and 1-methoxypropyl acetate-2.

Further constituents of the invention used

coating agent

The coating compositions used in the process according to the invention may advantageously contain photoinitiators (PI).

Suitable photoinitiators are, in particular, those from the group consisting of alpha-hydroxy ketones, alpha-amino ketones, phenylglyoxylates, benzyldimethylketals, monoacylphosphines, bisacylphosphines, phosphine oxides, metallocenes and iodonium salts. Preferred examples include 1-hydroxycyclohexyl phenyl ketone (Irgacure® 184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (Irgacure® 1173) 2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl} -2-methyl-propan-1-one (Irgacure® 127), 2-hydroxy-1- [4- (2-hydroxy-ethoxy) -phenyl] - 2-methyl-1-propanone (Irgacure 2959), methylbenzoylformal (Darocure® MBF) phosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) (Irgacure® 819) and diphenyl- (2,4,6-trimethylbenzoylphosphine oxide (Lucirin® TPO ).

In order to ensure a particularly good course of the coating and thus to obtain particularly smooth surfaces, commercially available leveling agents, such as, for example, Byk® 333, BYK® 310, can be added to the coating material that can be used according to the invention. will give. By such additives, the surface tension of the UV coating is lowered, so that a good wetting of the substrate is ensured under appropriate application conditions. Advantageously, the coating compositions contain leveling agents which contain one or more ethylenic double bonds which can react with the ethylenic double bonds of the binder during the curing process. An example of such a preferably used leveling agent is called Byk UV 3570.

If necessary, it is also possible to use adhesion promoters which ensure permanent intermediate adhesion to the substrate (for example polycarbonate) and / or primers. Examples of this class of additives are chlorinated polyolefins, acidic polyesters or phosphoric acid adducts. If necessary, the use of air vents is necessary to avoid cookers on the paint surface. For this purpose, commercial deaerators such. Byk-A 500, Byk-A 50, Byk-A 515, BYK 390, BYK 306, BYK 315 and BYK 356.

In addition to the abovementioned constituents, the coating compositions used in the process according to the invention may contain further clear-coat additives, such as, for example, wetting agents.

If required, the coating compositions used according to the invention may contain one or more light stabilizers as further additives typical of the clearcoat. Suitable are the light stabilizers commonly used, in particular based on UV absorbers and / or sterically hindered amines (HALS). The coating compositions used according to the invention preferably contain less than 6% by weight, in particular less than 0.1% by weight, in each case based on the total weight of the components (A1), (A2), (A3), (B), (C1), (C2) and (C3), light stabilizers. Most preferably, they contain no light stabilizer.

The components (A), (B), (PI) and the clear-type additives can be added to the coating composition used in the process according to the invention in dissolved or dispersed form. The solvents and / or reactive diluents used for these components are, as far as the complete coating composition is concerned, assigned to the reactive diluent (C) or the solvent. That is, component (C) also includes the reactive diluents which enter the coating agent via the other components.

Preferably, the inventively used

coating agents

(i) 30 to 60 wt .-%, preferably more than 40 to 50 wt .-%, based on the total weight of components (A1), (A2), (A3), (B), (C1), (C2 ) and (C3), the nanoparticles (B),

(ii) 15 to 40% by weight, preferably 20 to 30% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3) , one or more urethane (meth) acrylates (A1) having on average 3 to 5 acrylate and / or methacrylate groups per molecule

(Iii) 0 to less than 10 wt .-%, preferably 0 to 5 wt .-%, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and ( C3), one or more urethane (meth) acrylates (A2) having on average more than 5 acrylate and / or methacrylate groups per molecule (iv) 0 to less than 10 wt .-%, preferably 0 to 5 wt .-%, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and ( C3), one or more urethane (meth) acrylates (A3) having on average less than 3 acrylate and / or methacrylate groups per molecule

(v) 55 to 80% by weight, preferably 65 to 77% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3) , one or more monomeric and / or oligomeric compounds (C1) having 4 acrylate and / or methacrylate groups per molecule other than components (A1), (A2) and (A3),

(vi) 0 to 15% by weight, preferably 3 to 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3) , one or more, of the components (A1), (A2) and (A3) different, monomeric and / or oligomeric compounds (C2) having 2 acrylate and / or methacrylate groups per molecule and

(vii) 0 to 15% by weight, preferably 0 to 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3) , one or more monomeric and / or oligomeric compounds (C3) having 3 acrylate and / or methacrylate groups per molecule other than components (A1), (A2) and (A3),

wherein the sum of the weight fractions of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3) is in each case 100% by weight.

If solvents are present, they may be present in an amount of up to 80% by weight, based on the total coating agent. Finally, the coating agent preferably contains

0 to 10, more preferably 1 to 6 and most preferably 2 to 4 wt .-% of one or more photoinitiators (PI), wherein the amounts are based on the total weight of the binder (A) plus the weight of reactive diluent (C), and

0 to 15, particularly preferably 0.5 to 10 and very particularly preferably 0.5 to 5 wt .-% of further clear varnish typical additives, wherein the amounts are in each case based on the total weight of the coating composition.

Plastic substrate

As polycarbonate or polycarbonate substrate in the present invention, both homopolycarbonates and Copolycarbona- te understood. The polycarbonates may be linear or branched in a known manner. Also, some of the carbonate groups of the homo- or copolycarbonates may be replaced by dicarboxylic ester groups or other polycarbonate-compatible groups. Preferred among the dicarboxylic ester groups are aromatic dicarboxylic ester groups. If the polycarbonates contain dicarboxylic acid residues in addition to carbonic acid residues, this is also referred to as polyester carbonates which, as stated above, likewise fall under the term polycarbonates. If dicarboxylic acid ester groups are present, they may be present in a proportion of up to 80 mol%, preferably 20 to 50 mol%. Polycarbonates can be prepared by all methods known from the literature. Suitable processes for the preparation of polycarbonates are, for example, the preparation of bisphenols with phosgene by the phase boundary process or the homogeneous phase process (pyridine process) or from bisphenols with carbonic acid esters by the melt transesterification process. These preparation methods are described, for example, in H. Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, Vol. 9, pp. 31 to 76, Interscience Publishers, New York, London, Sidney, 1964. The production methods mentioned are also described in D Freitag, U. Grigo, PR Muller, H. Nouvertne, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, pages 648 to 718, and in U. S. Pat.

Grigo, K. Kircher and PR Müller "Polycarbonates" in Becker, Braun, Kunststoff-Handbuch, Volume 3/1, polycarbonates, polyacetals, polyesters, cellulose esters, Carl Hanser Verlag Munich, Vienna 1992, pages 117 to 299. The melt transesterification process is particularly in H. Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, pp. 44 to 51, Interscience Publishers, New York, London, Sidney, 1964, and in DE 10 31 512 A, US 3 022 272 , US Pat. No. 5,340,905 and US Pat. No. 5,399,659. The polycarbonates prepared by the processes described above have a weight-average molecular weight Mw of preferably from 12,000 to 400,000 g / mol, in particular from 18,000 to 80,000 g / mol and very particularly preferably from 22,000 to 60,000 g / mol.

The plastic substrates may also consist of polymethylmethacrylate (PMMA). Particularly preferred are transparent polycarbonates or polycarbonate substrates, preferably with a transmission> 80% of the visible light.

The plastic substrates can be present in any desired spatial form. In particular, the method according to the invention is suitable for coating housings of electronic components, such as, for example, mobile phone cases, smartphones, iPhones, electronic organizers, MP3 players, iPods, laptops, computers, digital cameras, video cameras, game consoles, game machines and the like.

Application and curing of the coating agent and coated plastic substrates

The application to the substrate is carried out by standard coating methods such as e.g. Dipping, flooding, spraying, brushing, knife coating, rolling, spraying, falling film application, spincoating or spinning.

Particularly advantageous is the application of the coating agent in a dipping or flooding process and by spray application with a low layer thickness and good flow.

For this purpose, the plastic substrate can be pretreated with a primer before application of the coating composition. Suitable primers are, for example, compositions as used in the process according to the invention, but which contain no nanoparticles (B). Preferably, the method according to the invention is carried out without primer treatment of the substrate. The process according to the invention is particularly preferably carried out in a single-layer process, which is called by applying only one layer of the coating agent directly on the non-chemically pretreated plastic substrate.

After application, if appropriate dripping and subsequent flash-off of the coating in the manner known to the person skilled in the art, the curing of the coating takes place. The curing can be effected by the action of high-energy radiation, for example UV radiation or electron radiation. The radiation sources used are preferably low-pressure mercury lamps, medium-pressure lamps, high-pressure lamps and fluorescent tubes, pulse emitters or Eximerstrahler, preferably light in a wavelength range between λ = 200 to 700 nm, more preferably from λ = 200 to 500 nm and most preferably λ = 200 bis Emit 400 nm. Furthermore, emitter systems are to be preferred which achieve a low heat load on the substrate by modifying the reflector. Such emitter systems are known as URS reflector systems of the company IST Metz GmbH. The radiation dose usually sufficient for UV curing is between 100 to 6000 mJ / cm ² , more preferably 1000 to 4000 mJ / cm ^2, and most preferably 2000 to 3000 mJ / cm ² . Depending on the distance between substrate and UV lamp, emitter power and reflector system find UV irradiation strengths between 100 to 6000 mW / cm ² , preferably 1000 to 4000 mW / cm ² and most preferably 2000 to 3000 mW / cm ² application.

The irradiation may be carried out under an oxygen-depleted atmosphere. "Oxygen depleted" means that the oxygen content of the atmosphere is less than the oxygen content of air (20.95 wt%). The atmosphere can basically also be oxygen-free, ie it is an inert gas. When Inert gases are carbon dioxide, nitrogen, noble gases or combustion gases. The preferred range of UV curing in an oxygen-depleted atmosphere is between 0.1 to 5% by weight of residual oxygen. Likewise, the irradiation of the coating composition can be carried out under transparent media such as plastic films, glass or liquids. The irradiation under an oxygen-depleted atmosphere has a favorable effect in particular on the later hardness and chemical resistance of the cured coating.

After curing, the coating and the substrate are transparent. The coating obtained on the substrate after curing and before loading has a haze value less than 1, preferably less than 0.8, in each case determined by means of the BYK-Gardner Hazegard plus C4725 device.

After a scratch load, measured by the Taber test based on ASTM 1044-05 and ASTM 1003-00, the loaded coating has a Haze value of <15%, preferably <10%, more preferably <8%, respectively determined using the BYK-Gardner Haze-gard plus C4725 device.

Another object of the invention are coated plastic substrates, in particular housing of electronic devices, which are obtainable by the inventive method. These may include, for example, mobile phone cases, smartphones, iPhones, electronic organizers, MP3 players, iPods, laptops, computers, digital cameras, video cameras, game consoles, game machines, and the like.

act. In the following the invention will be explained in more detail by means of examples.

example 1

Production of a coating B1 according to the invention

5.0 g of n-butanol, 16.81 g of isopropanol, 8.2 g of ethanol are mixed in a brown glass. Subsequently, 1.4 g of Irgacure® 184 (commercial photoinitiator from Ciba Specialty Chemicals, 1-hydroxycyclohexyl-phenyl-ketone) are added with stirring. 8.5 g of Desmolux® VP LS 2308 (unsaturated, aliphatic, essentially isocyanate-free, polyurethane acrylate based on the isocyanurate of hexamethylene diisocyanate and hydroxyethyl acrylate having a hydroxyl content of about 0.5% in accordance with DIN 53 240/2 and a average content of 3 to 4 acrylate groups per molecule from Bayer Material Science AG, about 80% in hexanediol diacrylate (HDDA), density 1.11 g / cm 3), 19.7 g SR 295 (pentaerythritol tetraacrylate from Sartomer), 0.4 Byk UV 3570 (commercial leveling additive from Byk-Chemie GmbH, solution of a polyester-modified acryl-functional polydimethylsiloxane) and 40.0 g Nanopol® C 784 (commercial SiO 2, average particle diameter of 20 nm, 50% in butyl acetate, available from Nano Resins AG) was added. After 15 minutes, the composition is applied to a polycarbonate sheet with a 36 μm bar blade. This is placed in the oven for 5 min at 80 ° C to flash off and then with UV light on an IST Lignocure system, equipped with two UV lamps (mercury lamps), both of which are set to 100% power . hardened. The coated polycarbonate sheet is cured at a dose of 2500 to 3000 mJ / cm 2.

Further application types

In the dipping application, a solids content of 50% by weight is preferably set. The solvent combination used is preferably a mixture of n-butanol, ethanol, ethyl acetate, isopropanol and solvent naphtha. After a dipping time of, for example, 5 seconds, a dripping time of about 1 minute and a flash-off time at about 80 ° C. of about 5 minutes, an IST Lignocure system (dose 1, 8 J / cm ² , intensity 0.3 W / cm ² ) curing to coatings of a layer thickness of 9 to 14 μιη performed.

In the case of application by flooding, it is preferable to set a solids content of 50% by weight. The solvent combination used is preferably a mixture of n-butanol, ethanol, ethyl acetate, isopropanol and solvent naphtha. After a dripping time of about 1 minute and a flash off at about 80 ° C for about 5 minutes, the curing becomes coatings by means of an IST Lignocure system (dose 1, 8 J / cm ² , intensity 0.3 W / cm ² ) a layer thickness of 9 to 12 pm performed.

When applied by spraying (nozzle: 1, 3 mm, air pressure 4 bar, spray distance 20 cm) is preferably a solids content of 40 wt .-% set. The solvent combination used is preferably a mixture of ethyl acetate, butyl acetate and isopropanol. After a flash off at about 80 ° C for about 5 minutes, by means of an IST Lignocure system (dose 3.9 J / cm ² , intensity 1, 4 W / cm ² ) the curing to coatings of a layer thickness of about 7 μιτι performed.

Measurement of turbidity:

The transparency is measured according to the test standard ASTM D1003. The initial Haze value before loading is shown in Table 1.

Test of liability:

To check the adhesion, the following tests are carried out on the coating of Example 1:

Adhesion test by means of adhesive tape tear (ASTM D 3359 and ISO 2409),

Cooking test: A bath filled with deionised water is brought to the boil. The prepared substrates are then immersed in the boiling water for 4 hours. After 4 hours, they are taken out of the water and briefly stored for cooling. Then a cross-hatch cut is made and the adhesion is tested with Tesa-demolition. If adherence has been achieved (i.e., GT <2), the varnish may be included in the water storage test (water storage according to ASTM 870-02 and ISO 2812-2).

Abrasion resistance test

The abrasion resistance of the surfaces was investigated by means of the Taber test. The Taber test and the subsequent haze measurement were carried out according to ASTM D 1044-05 and

ASTM D 1003-00, whereby the samples are not stored in standard atmosphere at 23 ° C and 50% relative humidity before the measurement were. The Haze after Taber was tested after 100, 300 and 1000 revolutions. The values are shown in Table 1.

Table 1: Test results of the coating of Example 1

Impact Test

The test of the resistance of the coating composition to sudden deformation (impact test) was tested in accordance with the standard DIN EN ISO 6272-1 DE. The test is carried out by a falling weight (300 g, mandrel 3/16) from a certain height (15 cm, 25 cm, 50 cm). The damage was assessed visually:

Starting from the point of impact, concentric cracks in the paint can be seen, which increase as the height of the fall increases and continue to expand. In all three cases, the substrate itself has no damage and peeling of the coating is not detectable, i. the adhesion between substrate and lacquer is still guaranteed.

Claims

claims:

1. A process for coating plastic substrates, in which a transparent coating agent comprising at least one radiation-curable urethane (meth) acrylate (A), nanoparticles (B), reactive diluents (C) and optionally solvents, is applied to the plastic substrate,

characterized in that the coating agent

(i) 30 to 60 wt .-%, based on the total weight of

Components (A1), (A2), (A3), (B), (C1), (C2) and (C3), the

Nanoparticles (B),

(iii) 0 to less than 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth ) - acrylates (A2) having on average more than 5 acrylate and / or methacrylate groups per molecule,

(iv) 0 to less than 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth ) - acrylates (A3) with on average less than 3 acrylate and / or methacrylate groups per molecule,

(v) 55 to 80% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more of the components ( A1), (A2) and (A3) different, monomeric and / or oligomeric Compounds (C1) with 4 acrylate and / or methacrylate groups per molecule,

(vii) 0 to 15% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C3) having 3 acrylate and / or methacrylate groups per molecule

A method according to claim 1, characterized in that the coating agent is applied to polycarbonate, on blends of polycarbonate with other plastics and / or on polymethyl methacrylate (PMMA).

A method according to claim 1 or 2, characterized in that the coating agent is applied to the housing of electronic devices.

Method according to one of claims 1 to 3, characterized in that the coating agent (i) more than 40 to 50% by weight, based on the total weight of the components (A1), (A2), (A3), (B), (C1), (C2) and (C3), of the nanoparticles ( B),

(ii) 20 to 30% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth) acrylates (A1) with on average 3 to 5 acrylate and / or methacrylate groups per molecule,

(iii) 0 to 5% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more urethane (meth) acrylates (A2) with on average more than 5 acrylate and / or methacrylate groups per molecule,

(iv) 0 to 5 wt .-%, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), one or more urethane (meth) acrylates (A3) with an average of less than 3 acrylate and / or methacrylate groups per molecule,

(v) 65 to 77% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C1) having 4 acrylate and / or methacrylate groups per molecule,

(vi) 3 to 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), of one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C2) having 2 acrylate and / or methacrylate groups per molecule and (vii) 0 to 10% by weight, based on the total weight of the film-forming components (A1), (A2), (A3), (C1), (C2) and (C3), one or more of the components ( A1), (A2) and (A3) various monomeric and / or oligomeric compounds (C3) having 3 acrylate and / or methacrylate groups per molecule

contains, where the sum of the weight portions of the film-forming

Components (A1), (A2), (A3), (C1), (C2) and (C3) each 100

Wt .-% is.

5. The method according to any one of claims 1 to 4, characterized in that the coating agent less than 6 wt .-%, based on the total weight of the components (A1), (A2), (A3), (B), (C1) , (C2) and (C3), contains light stabilizers.

6. The method according to any one of claims 1 to 5, characterized in that the coating agent as component (C1) pentaerythritol tetraacrylate and / or Ditrimethylolpropantetra- acrylate.

7. The method according to any one of claims 1 to 6, characterized in that the coating composition contains as component (C2) hexanediol diacrylate.

Method according to one of claims 1 to 7, characterized in that the coating agent contains as component (A1) one or more urethane (meth) acrylates (A1) having on average 3 to 4 acrylate and / or methacrylate groups per molecule.

9. The method according to any one of claims 1 to 8, characterized in that the coating composition contains as component (A1) one or more aliphatic urethane acrylates (A1). 10. The method according to any one of claims 1 to 9, characterized in that the coating agent contains as component (A1) one or more aliphatic urethane acrylates (A1) based on the isocyanurate of hexamethylene diisocyanate. 11. The method according to any one of claims 1 to 10, characterized in that the coating agent as component (A1) one or more aliphatic urethane acrylates (A1) based on the isocyanurate of hexamethylene diisocyanate and as a reactive thinner (C) a mixture of (C1) Pentaerythritol tetraacrylate and (C2) hexanediol diacrylate.

12. The method according to any one of claims 1 to 11, characterized in that the coating agent is applied directly to the plastic substrate.

13. Coated plastic substrates obtainable by a process according to one or more of claims 1 to 12.

14. Coated plastic substrates according to claim 13, characterized in that they are housings of electronic devices.

15. Coated housings of electronic devices according to claim 14, which are mobile phone shells, smartphones, iPhones, electronic organizers, MP3 players, iPods, laptops, Computers, digital cameras, video cameras, game consoles, gameboys, trades.